From viewpoints of energy saving and downsizing of image forming apparatuses, a toner is desired to have good fixability to keep heating of a fixing roller at a minimal level. Typically, in preparation of a toner having excellent low-temperature fixability, a binder resin having a low melting point or a low glass transition point, or a releasing agent having a low melting point is often used. However, there is a problem that when such a toner is preserved at high temperatures, toner particles included in the toner tend to agglomerate. When toner particles agglomerate, a charge amount of the agglomerating toner particles decreases more easily than a charge amount of toner particles that are not agglomerating.
Also, in order to improve charge stability of a toner, a toner including toner particles that contain a reduced amount of alkali metal elements in surfaces thereof is sometimes used. For example, Patent Literature 1 discloses a toner including toner particles in which hydrophilic polar groups are present at surfaces thereof and an amount of alkali metal elements present in the surfaces is reduced.